olives growing on a branch

The olive fruit is the greatest cure for any problem in life
- Solon


Winter fruit harvests are few and far between but I’ve just spent a very pleasant few hours helping friends with their annual olive harvest – a calm, clear winter’s day spent in the sun, feeling very much like a modern-day peasant woman. It was a great opportunity to meet some new people and the conversation flowed as we stripped fruit from cascading branches with our garden-gloved hands onto netting underneath our feet. Teams of three or four people can denude a tree of olives in no time, and the crates filled up surprisingly quickly. Fuelled by hot cups of tea, slabs of cake and a restorative bowl of soup at lunchtime, our work was complete by early afternoon.

Thanks to drought conditions in the Mediterranean region in the last growing season, the olive crop from the recent harvest has yielded a staggering 50% lower output than usual. Spain, one of the main olive oil producers, was particularly hard-hit, so we can expect the cost of oil here to soar in the coming months – now might be a good time to stock up, as most of the oil on supermarket shelves is imported. New Zealand has an established olive industry, but we only produce about 10% of the local consumption volume of oil - much of this is a premium, boutique product, which places it out of the reach of many and the high quality of the extra virgin oils produced means they are more suited to finishing purposes, dressing food, rather than day-to-day high heat cooking.

Although you would need a reasonable number of trees in the backyard to keep yourself in olive oil, you could think like my friends and team up with others to collectively harvest and process your olives (most press companies have a minimum processing quantity of 200 kg). The amount of oil extracted varies with the season and variety but is usually somewhere between 9-15%, so you’re looking at about one litre of oil from every 10 kg of olives. However, don’t forget you can also brine your own table olives, this takes relatively little effort and the cost of additional ingredients is minimal. Martini lovers rejoice, and you can keep yourself in tapenade and hors d'oeuvres as well. If you already have olive trees planted for ornamental reasons, you may already be looking at them in a different light. No wonder Solon, the ancient Greek statesman and lawmaker credited with laying the foundations for Athenian democracy also decreed the death penalty for murdering an olive tree.

Olives: a short family history

It’s hard to find a tree with more noble ancestry (think the wreaths adorning the heads of Olympians, the oil that anointed the heads of many a king and that keeps the Olympic flame burning) and Biblical connections (the olive branch brought back to Noah by the dove, or proffered in peace) than the olive. Along with wheat and grapes, the olive forms the trio of staple crops of the Mediterranean. Belonging to the Oleaceae, not surprisingly known as the olive family, close relatives include ornamentals such as lilac, jasmine, the bright yellow harbinger of spring forsythia, and the rather toxic, historically-used-for-hedging but now best avoided privet. Olea europaea, the European olive, is most commonly found in the countries of the Mediterranean Basin, where it has been grown since the 8th century BC, but interestingly is also native to Asia and Africa. Commercial cultivation now extends throughout Oceania, North and South America and South Africa as well. Of the total worldwide olive crop, about 80% is used for oil production and the remaining 20% for table use, with the main players being Spain, Italy and Greece in the Mediterranean; Turkey; and the North African countries Tunisia and Morocco. The arrival of olives in New Zealand is thought to predate 1835, as Charles Darwin noted their presence when he visited northern New Zealand in December 1835. The next recorded details were of plantings in the Auckland region in 1843. Between 1860 and 1880 both Sir George Grey and a gentleman by the name of Logan Campbell made individual (unsuccessful) attempts to establish and olive industry. In 1877 a report on the suitability of olives as a potential crop for New Zealand was submitted to parliament, but fell on deaf ears. Almost 100 years were to pass before the first official grove was planted in Marlborough by industry pioneer Gidon Blumenfeld in 1980.

Olives are slow-growing trees and give hard, close-grained timber that is prized for woodworking; the golden-coloured wood makes excellent kitchen utensils and chopping boards, being stain and odour-resistant. Due to the holy nature of the olive tree, the wood is often used to make religious items, and Solon need not worry – given the mighty age an olive tree can reach, it’s not always necessary to cut down the entire tree to harvest timber, as a side branch may give all that is necessary. Olive wood is also a great option for smoking food as it is clean burning, produces little ash and gives food a light, nutty, smoky flavour. I’ve read it’s a good option for fuelling wood-fired pizza ovens for a particularly authentic flavour! The olive’s graceful form and elegant silver-grey foliage lend it well to landscaping (as a hedge or screen) and as a specimen tree – espalier, topiary and pot culture are also options. There is also a diminutive shrubby non-fruiting form (O. europaea ‘Montra’, the dwarf or little olive) which is particularly suited to hedging.

On the supermarket shelf you’ll find olive leaf extract in various forms for helping banish colds and flu, and the uses for olive oil extend far beyond the kitchen – many Kiwis will remember the days when you could only purchase it from the chemist for medicinal purposes! As well as being an excellent source of healthy monounsaturated fat and a quintessential part of the much-touted Mediterranean diet, the oil is a great skin and hair tonic and all-round anti-inflammatory.

Suitable climates and growing conditions

Not surprisingly, olives will do best in areas where the climate mimics the Mediterranean: hot, dry summers and cool winters. Where you find wine grapes growing, you’ll likely find olives too. There are established commercial plantings in most areas of the country apart from Southland and the West Coast, the former not having the long, warm summers required to ripen the fruit and the latter being a bit too wet and humid. In most other instances, cultivar selection to match the climate can eliminate suitability issues. Mature trees can withstand winter frosts down to about -8 to -12°C, and most cultivars have an average winter chilling requirement of 200-300, and sometimes up to 500 hours.

In New Zealand, where are soil types are reasonably fertile and there is adequate moisture year-round, commercial growers who prune and harvest mechanically will plant trees spaced at three metres, with six metres in between rows. Traditionally, spacings were greater, up to 6 x 6 metres and I found some early advice that even recommended 10 metres between trees. The advantage of these larger spacings is that they do allow for a more natural tree shape, which is probably advisable if you only have a couple of specimen-type trees on your property. Olives will easily grow to 10 metres or more in height and a similar spread, so careful training and canopy management will be necessary if you plan to hand harvest. Olives are extremely long-lived, with 1,000 plus year old examples not uncommon overseas. The olive trees in the Garden of Gethsemane (gethsemane being the Aramaic word for olive press) have been carbon dated to over 1,000 years old.

Vegetatively propagated plants from cuttings or grafting should fruit within two or three years of planting and seedlings about five to seven years after planting. Growing olives from seed isn’t advised as they will likely revert back to wild types, so cut your losses and purchase plants of known cultivars from a reputable nursery. Some cultivars are noticeably difficult to propagate (Kalamata, Uovo di Piccione) and their availability may be limited, so place your order early to avoid disappointment if you have your heart set on a particular variety!

Olives flower in mid-late spring and produce either male flowers or bisexual flowers. Many are self-fertile, but others require a polliniser variety close by for cross-pollination, with the commercial standard being 10% of trees in the grove being pollinisers. Pollination is predominantly by wind, assisted by insects. It is generally 6-8 months between pollination and fruit maturity, with harvest taking place from late autumn to well into winter. The fruit holds well on the tree, extending the harvest window.

Site selection and planting

It’s best to plant olive trees in winter or early spring. Full sun with some shelter is ideal – New Zealand is quite a bit windier than the Mediterranean and young trees will definitely require protection and potentially staking, with wind tolerance increasing with age. They are reasonably tolerant of coastal conditions (I read some anecdotal evidence that in Greece, the trees start to sulk a bit if they’re grown too far from the sea). High humidity increases disease pressure and overly warm winters (without sufficient winter chill) result in adequate tree growth but little to no fruit set.

Olives are pretty adaptable when it comes to soil type – cold, waterlogged conditions are the only major situation to steer clear of. As with all fruit crops, they will do best in fertile, well-drained soils but can also thrive in sandy, stony and clay soils where others will curl up their toes.

Culture and care

Olives are reasonably drought-tolerant and can survive on drier, lighter soil types that other crops can’t produce on. That said, adequate moisture is important for young trees in the establishment phase and particularly important for producing trees at flowering/fruit set. A small amount of irrigation during summer will be of benefit in dry years, particularly for table olives as it will help increase the size of the fruit. Olives being produced for oil don’t need so much, as although less water will mean smaller fruit, it won’t change the oil content of the fruit.

In terms of fertiliser requirements, olives aren’t heavy feeders and one application of general fertiliser during flowering/fruit set and a foliar feed (potentially a seaweed preparation) is all that is necessary. Calcium and boron are the most common deficiencies in New Zealand olive growing regions and boron deficiency can have a significant effect on fruit set. It also causes a distinctive deformation at the tip of the fruit known as ‘monkey face’. Apply compound fertilisers prior to forecast rainfall or water in after application – follow the bag directions, the general rate is 0.25-0.5 kg per year of tree age, up to a maximum of 5 kg/tree at maturity. Spread about a cupful per square metre under the tree, right out to the dripline.

Pruning

Prune your olives after the harvest is complete – if you are in a particularly cold region, avoid midwinter to avoid unnecessary frost damage to the tree – the bulk of the foliage has protective benefits. It has been noted that three-yearly pruning may help avoid the biennial bearing that olives are somewhat prone to. An open vase shape suits olives well as it encourages good airflow and light penetration. Aim to choose about three to five main leaders in the first few years of establishment, removing any branches that are in unsuitable positions. Suckers and low-growing branches can be removed to give a clean trunk within a metre of the ground. Olives fruit on one-year-old wood, so you can cut back the tips of stems to encourage the production of lateral growth that will produce fruit.

Pests, diseases and what to do about them

Olives are generally quite hardy but there are a few issues to watch out for. Peacock spot, caused by the fungus Spilocaea oleagina is a common problem, resulting in concentric ring-shaped lesions on the upper surface of the leaves and also on the fruit. Affected trees can be treated with a copper fungicide spray in autumn and winter, after rainfall. Some cultivars have a degree of resistance. Phytophthora root rots can also be an issue on poorly-drained sites and recurring infections may be a sign that the land is unsuitable for olive cultivation. Olive knot, caused by the rain-spread bacterium Pseudomonas savastanoi (olive knot) and P. savastanoi pv. savastanoi (oleander knot) results in knot-like cankers on branches and enters through pruning wounds and areas of damaged bark. Again, some varieties have a degree of resistance. It is advisable to dig out and burn any affected trees.

In terms of insect pests, leafroller caterpillars can cause growing tips to become fused together with webbing and the sap-sucking black scale insect Saissetia oleae can cause unsightly black crusting on the tree’s limbs, followed by black sooty mould which develops anywhere the insect leaves its sticky exudates. A white mineral oil spray applied mid-summer will deal to the scale when the juvenile life stages are mobile and vulnerable.

Rabbits can cause significant ringbarking and destruction of newly-planted young trees, so invest in some plant guards and/or other control measures – there are also repellent sprays available. And lastly, birds just love to feast on ripe olives and can strip a tree in next to no time. Home growers with small numbers of trees are advised to net their crops.

Varieties: My top picks

Barnea (Israel) – a vigorous heavy cropper, not prone to biennial bearing. Suitable for pickling and oil, medium size fruit with a pointy end. Picholene and Manzanilla are suitable pollinisers.
Frantoio (Italy) – a high yielding, well-flavoured Tuscan oil cultivar that can also be pickled when green. Hardy, vigorous and disease-resistant. Pendolino is a suitable polliniser.
Leccino (Italy) – vigorous, hardy and cold-tolerant. Naturally resistant to peacock spot. A high-quality oil variety, requiring Pendolino or Frantoio as a polliniser.
Kalamata (Greece) – a well-known table olive that also produces high-quality oil. A vigorous, upright tree. Requires Manzanilla or Koroneiki as a polliniser. Tricky to graft, so availability of plants might be limited.
Manzanilla/Manzanillo (Spain) – an early, heavy-cropping oil and table olive. Smaller trees, not so cold-tolerant. Frantoio and Uovo di Piccione are suitable pollinisers.
Uovo di Piccione (Pigeon’s Egg) (Italy) – a large pickling variety, borne on small, slow-growing but shapely trees. Can be a heavy cropper. A handy polliniser for other varieties but susceptible to peacock spot. Another hard-to-propagate variety.

What to do with your crop

If you plan to harvest for oil, talk to your local press and book a slot well in advance. They may also be able to connect you with other small growers for a combined pressing if you only have a small crop.

Brine-cured olives

If you’ve ever tried a fresh raw olive, you’ll know they taste as bitter as hell. They require curing to draw out the bitterness, caused by the chemical oleuropein, a phenolic compound present in every part of the olive fruit and its leaves. Harvest as many fresh, unblemished olives as you desire – the larger the better. I wash mine in the sink and pick through them at the same time. You can sort based on colour if you want to be fancy. Most recipes recommend cutting a slit, or at least pricking holes in each individual olive but I don’t have the time or patience and being lazy works just fine for me.

Prepare a brine solution in a large non-reactive container (plastic, glass or stainless steel) using plain, non-iodised salt (1 part) and water (10 parts), so 100 g salt to every litre of water. Place the olives in your curing vessel/s (I use large three-litre glass jars from delicatessens which used to hold sundried tomatoes and the like) and cover with the brine solution. Place a china dish or glass jar of water on top of each container to keep the olives fully submerged under the brine and throw a tea towel over the top to keep out dust and bugs. Leave for 4-7 days, keeping an eye out for mould developing on the surface, then drain off the brine and replace with fresh solution. After about four weeks of following this process, try an olive and see what the bitterness levels are like. Curing can take six weeks or more, it all depends on the olives you are using.

When the bitterness level is to your taste, sterilise some jars and unblemished lacquered lids. Make up yet more fresh brine solution. Drain the olives and pack into jars, adding a tablespoon of vinegar (white, cider or wine) to each. Top right up with brine and a finally a layer of olive oil to seal, before screwing on sterilised lids. Store in a cool, dark place and store jars in the fridge once opened.

The olives will keep for several years like this and improve markedly with age. To use, soak the olives in fresh cold water for 24 hours, rinse and place in your favourite marinade of herbs, garlic, chilli or lemon, plus some olive oil and vinegar. Experiment until you find your olive-seasoning zenith!

Tapenade

I found a rough recipe scribbled in a notebook and made a batch of this the other day. I think the inclusion of anchovies is traditional but I’m not a fan – feel free to add in a few fillets if you wish.
Throw in the food processor: 

  • About 200 g pitted olives (invest in a cherry/olive pitter to make the task bearable)
  • ¼ cup capers, drained
  • A small handful of fresh thyme leaves
  • A couple of cloves of garlic
  • The juice of a lemon
  • Ground white pepper – to taste
  • And enough olive oil to make a thick, spreadable paste.

This is a great spread to include on a platter with contrasting colour dips/spreads e.g. tapenade made with black olives, muhammara (roasted red pepper and walnut dip) and green basil pesto. I often make batches of each and freeze portions in small containers for quick entertaining or snacking solutions.



Anna-Marie Barnes is an active member of the New Zealand Tree Crops Association who endeavours to grow and preserve as much of her own fresh produce as possible. When the weather’s no good for gardening, she can usually be found inside working on a batch of homemade cheese or soap.

The New Zealand Tree Crops Association is a voluntary organisation promoting interest in useful trees, such as those producing fruit, nuts, timber, fuel, wood, stock fodder, bee forage and other productive crops. Find out more about the NZTCA here: https://treecrops.org.nz/

Disclaimer: the information supplied above is of a general nature and provided as reference material only. In regards to pest and disease control, please consult your agrichemical consultant for suitable products, application rates and further region-specific information.

Image credits
Green olives - Van3ssa 🩺 Zheki 🙏 Dazzy 🎹 via pixabay.com
Olive fruit - Karl Oss Von via pixabay.com
Olive grove - Tom/analogicus via pixabay.com
Olives & oil - 1195798-1195798 via pixabay.com